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: Blow off valves (pop off valves, bypass valves, recirculating valves) blow off excess compressed air that has been created by the turbos. Recirculating valves take it a set further and recycles the excess air back into the intake. Under acceleration, instead of the excess air being pushed back into the turbo backwards it will expell the excess air and the turbos will continue to spin forwards. Pop-off valves are really "saftey boost" valves. They're set to "pop-off" at a certain psi (that you set) so that if the wastegates fail or whatever, you have a saftey mechanism of releasing boost so that you never overboost. Recirculating valves and blow-off valves serve the function of relieving compressor surge. Think of compressor surge as this: you're accelerating in 2nd, turbos singing, boosting 17 psi when you get up to the redline and you need to shift to 3rd. What do you do? Floor the clutch, lift off the gas, shift. Well, when you lift off the gas, the throttle plates shut down completely and the boost that was going from your turbo to your intake is now trapped inbetween. This "compressor surge" makes it's way back to the turbo as a shock wave and can cause the turbo to reverse (as John mentioned above). This is what the blow-off/recirculation valves do. They release this surge of air either into the atmosphere (BOVs) or back into the intake (recirc. valves). Regards,
Ben(Miami)
Black 1992 Stage VI+ TT
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